This invention relates to a novel process for solid-liquid separation of contaminants, colorants and other solid suspended matter from a colloidal-suspension to yield a clarified effluent and an apparatus therefor.
According to conventional methods for the separation of solids suspended in a suspension, an inorganic metal salt flocculating agent, for instance, aluminum sulfate or ferric chloride is added to the suspension so as to flocculate colloidal particles, of the suspended matter, promote coagulation of the flocced particles and increase the precipitation rate thereof so as to facilitate separation of the solids from the suspension.
When the precipitation rate of the solids is to be increased, conventionally an organic high molecular weight flocculating agent is incorporated in the suspension to increase the coagulum of flock and thus accelerate the precipitation rate thereof.
However, floc particles of the colloidally suspended solids thus formed in accordance with these customary methods do not exhibit strong coalescent bonds between particles themselves, they are excessively hydrated, have a low density, and concomitant slow precipitation rate in spite of the bulk and size of floc particles thereof. It is a further disadvantage of these prior processes that the floc particles produced therefrom are inadequately dehydrated. In consequence of the foregoing, none of these conventional processes have satisfactory hydroextraction properties. Furthermore, the quality of the water obtained is poor.
To overcome the shortcomings of these conventional processes, it has been proposed to treat a highly concentrated suspension, viz., a pre-treatment process for a sludge comprising feeding a suspension containing suspended solids at a concentration of 10 g/l - 500 g/l into a vessel, adding thereto a high molecular weight flocculating agent, for instance, a high molecular weight polyacrylamide, a partially hydrolyzed compound thereof and sodium polyacrylate, in the amount of at least 0.2 g-polymer per kg-solid, maintaining the concentration of the suspension inside the vessel at 30 - 500 g/l, and rotating the suspension at an outer peripheral speed of 0.5 - 3 m/sec so as to granulate the suspended solids and separate them from the mother liquor.
According to the described method, the suspended solids agglomerate into mass of finely divided particles, thereby ensuring an improved dehydration and exhibiting satisfactory hydroextraction properties. This method, however, is not free from major problems yet to be remedied. Namely, the method is not effectively applicable to a suspension having a solids concentration less than 10 g/l.
In accordance with this prior method, agglomerated finely divided particles are not formed in a suspension wherein the solids concentration is less than 10 g/l. In the past, it has therefore, been necessary in practicing this method to employ conjointly therewith a dehydration-precipitation procedure to thereby flocculate the colloidal solids and separate condensate therefrom by increasing the solids concentration to 10 g/l or more. Accordingly, this prior modified method is impractical for treating a mother liquor containing a relatively small quantity of colloidally-suspended solids wherein the solids concentration is less than 10 g/l, such as, for instance, may be formed in river water, lake water and the like. Furthermore, the method does not provide for separation of granulated particles from supernatant so that a clarified elluent does not result.
As is evident therefore, a method for granulating a colloidal suspension at low cost and providing a clarified effluent free of the colloidally-suspended particles would be highly desirable.